1. Field of the Invention
The present invention relates generally to power supplies for electronic equipment, and more particularly to power supplies in which electro-mechanical means are employed to provide hold-up times in the range of 0.1 to 10 seconds, together with excellent rejection of power line transients, the ability to deliver power several times rated output for short periods, and the option of operating at high line power factor from single-phase AC lines. Hold-up time is defined as the amount of time for which a power supply can sustain its output within regulation limits following loss of AC input power.
2. Description of the Prior Art
All electronic equipment requires direct current electricity ("CDC") for its internal operation. Such equipment includes computers, communications systems, televisions, radios, medical electronics devices, military electronics systems, and more. In most of these cases, the internal DC is obtained by conversion from a source of alternating-current electricity ("AC"), either in single-phase or three-phase form. The subsystem which is used to convert the incoming AC to the point-of-use DC is referred to as the "power supply".
Usually, the power supply is located internal to the piece of equipment it supplies. Because the AC power may fluctuate, or may vanish for short intervals, equipment installations often incorporate ancillary devices to mitigate or eliminate the effects of these supply variations. Devices which mitigate power fluctuations are generally referred to as power conditioners, and devices which provide an alternate source of power when the AC is temporarily absent are referred to as battery backup systems or uninterruptible power supplies (UPSs).
The industry which manufactures power conversion equipment is structured in terms of providing power supplies, power conditioners, and battery backup systems. One of several insights which motivate the present invention is that the fundamental need of electronic equipment is for direct current electricity, rather than for power supplies, battery backup systems, or power conditioners. Another such insight is that the existing industry structure derives from the available technologies for electricity storage.
It is widely accepted that three important performance measures for power supplies are:
1) Reliability, usually expressed in terms of mean-time-between-failure (MTBF), PA1 2) Power Density, expressed in rated power output per unit volume, typically in watts per cubic inch (W/in3), PA1 3) Cost, usually expressed in dollars per watt ($/W) of rated output power. PA1 1) Holdup Time, as defined above, measured in seconds or minutes, PA1 2) Volume, expressed either in joules per cubic inch (J/in3) or in W/in3, PA1 3) Cost, expressed in $/J, PA1 4) Dependability, measured in terms of the probability of failing to deliver the required energy when called upon. (One faulty battery cell in a series connection can cause a UPS to malfunction, and may not be detected until the UPS is needed). PA1 1) Isolation capability, i.e., the ability to protect the electronic equipment from rapid fluctuations (noise spikes) on the AC power line, PA1 2) Peak Power Capability, i.e., the ability to deliver power several times rated output for short periods, PA1 3) High Power Factor, i.e., the ability to extract power from the AC line smoothly, with the current waveform matching the voltage waveform, rather than with a pulsating current waveform.
For Battery Backup Systems, the following performance measures are of primary concern:
Other requirements for a power supply include:
FIG. 1 lists these performance measures, and shows how existing commercially-available hardware performs relative to these figures of merit. In summary, the combination of power supplies and UPSs falls to provide an ideal technical solution to all of the requirements for a system whose primary purpose is to deliver direct current electricity to an item of electronic equipment.
FIG. 2 provides an explanation. In the upper part of this figure, rated output power is plotted against holdup time, both scales being logarithmic. The left-hand region of the chart shows the capabilities of conventional power supplies, while UPSs appear at the right-hand side, leaving a void in the center. Conventional motor-generators make an inroad into the void at higher power levels, but suffer the disadvantages of excessive physical bulk and insufficient holdup time to cover the majority of outages. In the lower part of FIG. 2, well-established statistical data are summarized in a plot of the percentage of power outages versus their duration, as experienced at most AC power outlets, worldwide. It can be seen that a holdup time of 1-2 seconds will cover almost all outages, whereas conventional power supplies are entirely inadequate in this regard. UPSs provide much more holdup than is necessary to cover the majority of outages, but still do not provide sufficient energy to cover all outages such as those lasting several hours or more. These inadequacies of the prior art are solved by the present invention.
FIG. 3 charts energy storage densities on a logarithmic scale for five energy-storing media. Three of these provide energy storage and retrieval directly in the form of electricity, these three being inductors, capacitors, and batteries. The fourth medium, small flywheels, permits electricity storage and retrieval when coupled to an electric motor. These four media are the only known means for storing and retrieving electricity directly. The fifth medium shown in FIG. 3, fossil fuels, is shown only by way of comparative reference.
The relative positions of capacitors (which are used for holdup energy in power supplies) and batteries (which are employed in UPSs) illustrate why there is a void region in the upper chart of FIG. 2. Another reason for this, not so obvious, is the fact that the quantity of batteries which are necessary for a UPS to meet its power output requirement will give a holdup time measured in minutes rather than seconds.
A motivating insight for the present invention is the fact that small flywheels in conjunction with electric motors and generators can provide a means to produce a power supply which has holdup times in the range 1 to 5 seconds (or more, or less, if desired), and which occupies very little more physical space than a conventional power supply. The present invention, however, goes far beyond the mere assemblage of conventional devices. A novel integration of elements via a unique mechanical arrangement provides a new class of electronic circuit device which is referred to as a dynamic transformer. When a power supply includes a dynamic transformer, it is referred to as dynamic transformer power supply or a floating state power supply.
FIG. 4 shows how dynamic transformer power supplies fill the void in the upper chart of FIG. 2. With a dynamic transformer power supply, an item of electronic equipment will not require an ancillary power conditioner or battery backup system in many applications where it otherwise would have.
FIG. 5 lists the performance measures given in FIG. 1, and shows that the dynamic transformer power supply overcomes the deficiencies of the prior art in means for supplying direct current electricity to electronic equipment.